Method and apparatus for sorting particles

ABSTRACT

A method and apparatus for sorting particles moving through a closed channel system of capillary size comprises a bubble valve for selectively generating a pressure pulse to separate a particle having a predetermined characteristic from a stream of particles. The particle sorting system may further include a buffer for absorbing the pressure pulse. The particle sorting system may include a plurality of closely coupled sorting modules which are combined to further increase the sorting rate. The particle sorting system may comprise a multi-stage sorting device for serially sorting streams of particles, in order to decrease the error rate.

RELATED APPLICATIONS

This application claims priority to divisional U.S. patent applicationSer. No. 10/940,143 entitled “Method and Apparatus for SortingParticles” filed Sep. 13, 2004, which is a divisional of U.S. patentapplication Ser. No. 10/179,488 entitled “Method and Apparatus forSorting Particles” filed Jun. 24, 2002 which claims priority to U.S.Provisional Patent Application No. 60/373,256 entitled “MicrofluidicSystem Including a Bubble Valve for Regulating Fluid Flow Through aMicrochannel” filed Apr. 17, 2002, the contents of which are hereinincorporated by reference.

FIELD OF THE INVENTION

The invention relates to a method and apparatus for the sorting ofparticles in a suspension, where the input flow path of a sorting modulecan be split into several output channels. More particular, theinvention relates to a particle sorting system in which a plurality ofsorting modules are interconnected as to yield an increased particlethroughput.

BACKGROUND OF THE INVENTION

In the fields of biotechnology, and especially cytology and drugscreening, there is a need for high throughput sorting of particles.Examples of particles that require sorting are various types of cells,such as blood platelets, white blood cells, tumorous cells, embryoniccells and the like. These particles are especially of interest in thefield of cytology. Other particles are (macro) molecular species such asproteins, enzymes and poly-nucleotides. This family of particles is ofparticular interest in the field of drug screening during thedevelopment of new drugs.

Methods and apparatuses for particle sorting are known, and the majoritydescribed in the prior art work in the condition where the particles aresuspended in a liquid flowing through a channel network having at leasta branch point downstream and are operated according thedetect-decide-deflect principle. The moving particle is first analyzedfor a specific characteristic, such as optical absorption, fluorescentintensity, size etc. Depending on the outcome of this detection phase,it is decided how the particle will be handled further with. The outcomeof the decision is then applied to deflect the direction of specificparticle towards a predetermined branch of the channel network.

Of importance is the throughput of the sorting apparatus, i.e. how manyparticles can be sorted per unit of time. Typical sorting rates forsorters employing flows of particle suspension in closed channels are inthe range from a few hundred particles per second to thousands ofparticles per second, for a single sorting unit.

An example of a sorting device is described in U.S. Pat. No. 4,175,662,the contents of which are herein incorporated by reference. In the '662patent, a flow of particles, cells in this case, flows through thecenter of a straight channel, which branches into two perpendicularchannels at a branching point downstream (T-branch). The enteringparticles are surrounded by a sheath of compatible liquid, keeping theparticles confined to the center of the channel. In normal conditions,the flow ratio through the two branches is adjusted so that theparticles automatically flow through one of the branches. In a sectionof the channel a characteristic of the particles is determined using adetector, which can be an optical system (detection phase). The detectorraises a signal, which is interpreted. When the detector detects aparticle possessing a predetermined characteristic in the decisionphase, a deflector is activated for deflecting the particle in adeflection phase. In this case, the deflector comprises an electrodepair, positioned in the branch of the channel where the particlesnormally flow through in the inactivated state of the deflector. By theapplication of current pulses, the aqueous liquid is electrolysed,yielding a gas bubble evolving between the electrode pair. As the gasbubble increases in size, the flow rate through this branch is reducedduring the evolving phase. After the current pulse is applied, thebubble growth stops and the gas bubble is carried along with the flow.As a result, the flow through the specific branch is momentarily reducedand the particle of interest changes paths and flows down the otherbranch.

The described device is effective for sorting particles, however oneserious drawback is that gas bubbles are created which potentially canaccumulate at certain points of the fluidic network or clog flowchannels, yielding erroneous sorting. Another drawback is that thegenerated gasses (mostly oxygen and hydrogen) and ionic species (mostlyOH⁻ and H⁺) influence the particles flowing through the branch with theelectrode pair. In addition, cells and delicate proteins such as enzymesare very fragile and can be destroyed by the fouling constituentsco-generated with the gas bubble. Another drawback is the complexity ofthe overall sorting apparatus. In particular, the micro electrodeconstruction is very complex to mount and assemble in the small channelsof the system. As a result, the cost of a sorting unit is relativelylarge.

Another example of a particle sorting system of the prior art isdisclosed in U.S. Pat. No. 3,984,307, the contents of which are hereinincorporated by reference. In the '307 patent, the particles areflowing, confined by a flowing sheath liquid, through the center of achannel. After passing a detector section, the channel branches to twochannels under an acute angle (Y-branch). Just before the branchingpoint, an electrically activated transducer is located in the channelfor deflecting a specific particle having an appropriate, predeterminedcharacteristic. The transducer described is a piezo actuator orultrasonic transducer, yielding upon electrical activation a pressurewave in the channel. The generated pressure wave momentarily disturbsthe flow in one branch thus deflecting the particle of interest into theother branch

Also in this device, as in the previous discussed device, the deflectoris incorporated within the channel system, resulting in relatively largecosts of construction. Another drawback is the deflector principle used.The generated pressure waves are not confined to the branching point,but will propagate upstream into the detector section as well asdownstream both branches and influence the overall flow through thechannel. This is particularly a drawback if sorters of this type areconnected either in series or in parallel as to build a sorter systemwith increased throughput. Pressure waves generated in one sorter canthen influence the flows and deflection of particles in neighboringsorter units.

Another disclosed sorter, U.S. Pat. No. 4,756,427, the contents of whichare herein incorporated by reference, is analogous to the sorterdisclosed the earlier discussed '662. In this case however, the flow inone branch is disturbed by momentarily changing the resistance of thebranch. The resistance is changed by changing the height of the branchchannel by an external actuator. In the preferred embodiment, thisexternal actuator is a piezo disc glued on top of the channel, causingit to move downwards upon activation.

Although the construction of the sorter described in the '427 patent isless complex as the previous sorter structures, it is still problematicto couple multiple sorter modules of the described type together toincrease the sorting rate. This is, as in the sorter described in '307because of the generated pressure waves causing interference with othersorter modules.

Another particle sorting device is described in U.S. Pat. No. 5,837,200,the contents of which are herein incorporated by reference. The '200patent describes a sorting device that uses a magnetic deflection moduleto classify or select particles based on their magnetic properties. The'200 patent further describes processing and separating individualparticle streams in parallel.

SUMMARY OF THE INVENTION

The present invention provides a method and apparatus for sortingparticles moving through a closed channel system of capillary size. Theparticle sorting system of the invention provides a sorting module thatcan be assembled at low cost while providing an accurate means ofsorting large amounts of particles per unit of time. The particlesorting system may include a plurality of closely coupled sortingmodules which are combined to further increase the sorting rate. Theparticle sorting system may comprise a multi-stage sorting device forserially sorting streams of particles, in order to decrease the errorrate.

The particle sorting system implements an improved fluidic particleswitching method and switching device according to the currentinvention. The particle sorting system comprises a closed channel systemof capillary size for sorting particles. The channel system comprises afirst supply duct for introducing a stream of particles and a secondsupply duct for supplying a carrier liquid. The first supply duct formsa nozzle to introduce a stream of particles into the flow of carrierliquid. The first supply duct and the second supply duct enter ameasurement duct, which branches into a first branch and a second branchat a branch point. A measurement region is defined in the measurementduct and is associated with a detector to sense a predeterminedcharacteristic of particles in the measurement region. Two opposedbubble valves are positioned in communication with the measurement ductand are spaced opposite each other. The bubble valves communicate withthe measurement duct through a pair of opposed side passages. Liquid isallowed to partly fill these side passages to form a meniscus thereinwhich interfaces the carrier liquid with the reservoir of the bubblevalves. An external actuator is also provided for actuating one of thebubble valves. When the external actuator is activated, the pressure inthe reservoir of the activated bubble valve increases, deflecting themeniscus and causing a flow disturbance in the measurement duct todeflect the flow therein.

When a sensing means in the measuring region senses a predeterminedcharacteristic in a particle flowing through the measurement region, thesensing means produces a signal in response to the sensedcharacteristic. The external actuator is responsive to the sensing meansto cause a pressure pulse in a compression chamber of a first bubblevalve to deflect the particle with the predetermined characteristic,causing the selected particle to flow down the second branch duct.

In one aspect, the invention comprises a method of sorting particlesincluding the steps of providing a measurement duct having an inlet anda branching point at which the duct separates into two branch ducts,conducting a stream of fluid into the duct inlet with a stream ofparticles suspended therein, such that the particles normally flowthrough a first one of the branch ducts and providing upstream from thebranching point two opposing side passages for momentarily deflectingthe stream in the duct. A first one of the side passages ishydraulically connected to a compression chamber of a first bubblevalve, which is acted upon by an external actuator for varying thepressure therein. A second of the side passages is hydraulicallyconnected with a buffer chamber of a second bubble valve for absorbingpressure variations. The method further comprises providing ameasurement station along the measurement duct upstream of the sidepassages for sensing a predetermined characteristic of particles in thestream and for producing a signal when the predetermined characteristicis sensed. The method further comprises the step of, in response tosensing the predetermined characteristic, activating the externalactuator for creating a flow disturbance in the duct between the sidepassages, thereby deflecting the particle having the predeterminedcharacteristics and causing the selected particle to flow down thesecond branch duct.

In further aspects of the invention, the particle sort rate isrespectively increased or the type of particles sorted being increased,by respectively connecting a plurality of sorting modules in parallel orserially connecting a plurality of sorting modules in a binary tree likeconfiguration.

According to one aspect of the invention, a particle sorting system isprovided. The particles sorting system comprises a first duct forconveying a stream of suspended particles confined in a carrier liquid,comprising an inlet, a first outlet and a second outlet, a sensor forsensing a predetermined characteristic in a particle, a side channel incommunication with the first duct, a sealed chamber positioned adjacentto the side channel, wherein the carrier fluid forms a meniscus in theside channel to separate the sealed chamber from the carrier fluid; andan actuator. The actuator modifies the pressure in the sealed chamber todeflect the meniscus when the sensor senses the predeterminedcharacteristic. The deflection of the meniscus causes the particlehaving the predetermined characteristic to flow into the second outletwhile particles that do not have the predetermined characteristic flowinto the first outlet.

According to another aspect of the invention, a particle sorting systemis provided. The particle sorting system comprises a first duct forconveying a stream of suspended particles confined in a carrier liquid,a sensor for sensing a predetermined characteristic in a particle and afirst side channel in communication with the first duct. The first ductcomprises an inlet, a first outlet and a second outlet. The particlesorting system further comprises a sealed actuator chamber positionedadjacent to the first side channel, wherein the carrier fluid forms ameniscus in the first side channel to separate the sealed chamber fromthe carrier fluid, an actuator for modifying the pressure in the sealedactuator chamber to deflect the meniscus when the sensor senses saidpredetermined characteristic and a buffer. The deflection of themeniscus creates a transient flow in the first duct which deflectsparticle having said predetermined characteristic to flow into thesecond outlet while particles that do not have said predeterminedcharacteristic flow into the first outlet. The buffer absorbs atransient flow in the first duct.

According to another aspect of the invention, a particle sorting systemis provided. The particle sorting system comprises a duct for conveyinga stream of particles in a carrier fluid, a sensor for sensing apredetermined characteristic in a particle and an actuator. The ductcomprises an inlet, a first outlet and a second outlet, wherein theparticles normally flow from the inlet into the first outlet. Theactuator selectively applies a pressure pulse to the suspension todeflect a particle in the stream of particles into the second outletwhen said predetermined characteristic is detected. The particle sortingsystem further comprises a buffer for absorbing the pressure pulse.

According to yet another aspect of the invention, a particle sortingsystem is provided. The particle sorting system comprises a duct forconveying a stream of suspended particles confined in a carrier fluid,comprising an inlet, a first outlet and a second outlet, wherein theparticles normally flow from the inlet into the first outlet, a sensorfor sensing a predetermined characteristic in a particle, an actuatorfor selectively applying a pressure pulse to the stream of suspendedparticles to deflect a particle in the stream of particles when saidpredetermined characteristic is detected, causing it to flow into thesecond outlet and a buffer for absorbing the pressure pulse. The buffercomprises a side channel in communication with the duct, a sealed bufferchamber adjacent to the side channel and a meniscus formed by thecarrier fluid at an interface between the sealed chamber and the sidechannel.

According to still another aspect of the invention, a particle sortingsystem is provided. The particle sorting system comprises a first ductfor conveying a stream of suspended particles confined in a carrierliquid, comprising an inlet, a first outlet and a second outlet, asensor for sensing a predetermined characteristic in a particle, a sidechannel in communication with the first duct, a sealed chamberpositioned adjacent to the side channel, wherein the carrier fluid formsa first meniscus in the side channel to separate the sealed chamber fromthe sealed chamber an actuator for modifying the pressure in the sealedchamber to deflect the first meniscus when the sensor senses saidpredetermined characteristic, whereby the deflection of the meniscuscauses a particle having said predetermined characteristic to flow intothe second outlet while particles that do not have said predeterminedcharacteristic flow into the first outlet and a buffer for absorbing thepressure pulse. The buffer comprises a side channel in communicationwith the duct, a sealed chamber adjacent to the side channel and a firstmeniscus formed by the carrier fluid at an interface between the sealedchamber and the side channel.

According to another aspect of the invention, a particle sorting systemfor sorting particles suspended in a liquid is provided. The particlesorting system comprises an inlet duct through which flows a liquidcontaining particles having a predetermined characteristic and particlesnot having a predetermined characteristic. The inlet duct branches intoa plurality of measurement channels which are operated in parallel andsimultaneously fed with the liquid, each measurement channel having asorting module and two outlet channels, and each sorting module having aswitch unit for distribution of particles having a predeterminedcharacteristic and particles not having a predetermined characteristicto said two different outlet channel. Each switch unit comprises atleast one sensor which detects and classifies the particles having thepredetermined characteristic, a side passage in communication with theinlet duct, a sealed chamber adjacent to and separated from the sidepassage by a meniscus formed by the liquid and an actuator controlled byeach said sensor arranged on each said switch unit for selectivelydeflecting the meniscus to deflect a particle having the predeterminedcharacteristic into one of said outlet channel. Each of the two outletchannels on each measurement channel is connected to a separate summingchannel for the particles having a predetermined characteristic andparticles not having a predetermined characteristic selectivelydistributed to it.

According to still another aspect of the invention, a particle sortingsystem for sorting particles suspended in a liquid is providedcomprising an inlet duct through which flows a liquid containingparticles having a predetermined characteristic and particles not havinga predetermined characteristic. The inlet duct branches into a pluralityof channels which are operated in parallel and simultaneously fed withthe liquid, each channel having a sorting module and two outletchannels, and each sorting module having a switch unit for distributionof particles having a first predetermined characteristic and particlesnot having the first predetermined characteristic between said twodifferent outlet channels. Each sorting module comprises at least onesensor which detects and classifies the particles having the firstpredetermined characteristic, and an actuator controlled by each of saidsensor arranged on each said switch unit for selectively deflecting aparticle having the first predetermined characteristic into one of saidoutlet channels. Each of said two outlet channels on each sorting moduleis connected to a separate summing channel for the particles having thefirst predetermined characteristic and particles not having the firstpredetermined characteristic selectively distributed to it. The systemfurther comprises at least one secondary sorting module connected to thesumming channel for the particles having the first predeterminedcharacteristic, each of said secondary sorting modules having a firstoutlet channel and a second outlet channel, a detector for sensingparticles and a switch unit for selectively deflecting a particle havinga second predetermined characteristic into one of said outlet channelsbased on a second predetermined characteristic.

According to another aspect, a particle sorting system is provided,comprising a plurality of parallel primary sorting channels throughwhich flows a stream of suspended particles confined in a carrierliquid. Each primary sorting channel has a detection region fordetecting a predetermined characteristic in a particle and a switchingregion for separating particles having the predetermined characteristicinto a first receiving channel from particles that do not have thepredetermined characteristic, which flow into a second receivingchannel. The system further comprises an aggregation region foraggregating the particles having the predetermined characteristic fromthe first receiving channels, and at least one secondary sorting channelin series with the plurality of parallel primary sorting channels forcollecting the selected particles from the plurality of first outletchannels and separating particles in the secondary sorting channelhaving the predetermined characteristic from other particles in thesecondary sorting channel.

According to a final aspect, a method of sorting small particles isprovided. The method comprises the steps of providing a closed ducthaving an inlet and a fork at which the duct separates into two branchducts, conducting a stream of liquid into the duct inlet with a streamof particles suspended therein, the particle stream normally flowingthrough a first one of the branch ducts surrounding the stream of liquidwith a particle free enveloping current of liquid to producesubstantially laminar flow and providing a measurement station along theclosed duct upstream of the fork for sensing a predetermined property ofparticles in the stream and for producing a signal when the property issensed. The method further comprises providing an actuator for applyinga pressure on the liquid and providing means for buffering pressurevariations in the liquid. The pressure buffering means cooperates withthe pressure applying means to result in a momentary deflection of theliquid streaming through the duct substantially perpendicular to thenormal direction of flow from the point where the pressure is appliedtowards the point where the pressure is buffered, causing the specificparticle having the predetermined property to flow into the secondbranch duct without eliminating the laminar flow.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a particle sorting system according to anillustrative embodiment of the invention.

FIGS. 2 through 4 illustrate the operation of the particle sortingsystem of FIG. 1.

FIG. 5 illustrates a particle sorting system showing alternate positionsfor the actuator chamber and the buffer chamber.

FIG. 6 illustrates the particle sorting system according to anotherembodiment of the invention.

FIG. 7 illustrates a bubble valve suitable for use in the particlesorting system of the invention.

FIG. 8 is a schematic diagram of the particle sorting system of anillustrative embodiment of the invention

FIG. 9 shows a particle sorting system for sorting parallel streams ofparticles.

FIG. 10 shows a particle sorting system binary tree-like configurationof sorting modules.

FIG. 11 illustrates a multi-stage particle sorting system for sortingparallel streams of particles in two stages.

FIG. 12 illustrates a parallel particle sorting system according to analternate embodiment of the invention.

FIG. 13 illustrates a parallel particle sorting system according toanother embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a particle sorting system for sortingparticles suspended in a liquid. The particle sorting system provideshigh-throughput, low error sorting of particles based on a predeterminedcharacteristic. The present invention will be described below relativeto illustrative embodiments. Those skilled in the art will appreciatethat the present invention may be implemented in a number of differentapplications and embodiments and is not specifically limited in itsapplication to the particular embodiments depicted herein.

FIG. 1 shows a schematic of a particle sorting system according to anillustrative embodiment of the invention. According to one applicationof the present invention, a particle sorting system 10 comprises aclosed channel system of capillary size for sorting particles. Thechannel system comprises a first supply duct 12 for introducing a streamof particles 18 and a second supply duct 14 for supplying a carrierliquid. The first supply duct 12 forms a nozzle 12 a, and a stream ofparticles is introduced into the flow of carrier liquid. The firstsupply duct 12 and the second supply duct 14 enter a measurement duct 16for conveying the particles suspended in the carrier liquid, whichbranches into a first branch 22 a and a second branch 22 b at a branchpoint 21. A measurement region 20 is defined in the measurement duct 16and is associated with a detector 19 to sense a predeterminedcharacteristic of particles in the measurement region 20. Two opposed ofbubble valves 100 a and 100 b are positioned in communication with themeasurement duct 16 and are spaced opposite each other. The bubblevalves 100 a, 100 b communicate with the measurement duct 16 through apair of opposed side passages 24 a and 24 b, respectively. Liquid isallowed to partly fill these side passages 24 a and 24 b to form ameniscus 25 therein. The meniscus defines an interface between thecarrier liquid and a gas in the reservoir of the associated bubble valve100. An external actuator 26 is also provided for actuating the firstbubble valves 100 a, which momentarily causes a flow disturbance in theduct to deflect the flow therein when activated by the actuator 26. Thesecond bubble valve 10 b serves as a buffer for absorbing the pressurepulse created by the first bubble valve 100 a.

The first side passage 24 a is hydraulically connected to a compressionchamber 70 a in the first bubble valve 100 a, so that if the pressure inthis chamber is increased, the flow in the measurement duct near theside passage is displaced inwards, substantially perpendicular to thenormal flow in the duct. The second side passage 24 b, positionedopposite of the first side passage 24 a is hydraulically connected to abuffer chamber 70 b in the second bubble valve 100 b for absorbingpressure transients. This second side passage 24 b co-operates with thefirst side passage 24 a to direct the before mentioned liquiddisplacement caused by pressurizing the compression chamber 70 a, sothat the displacement has a component perpendicular to the normal flowof the particles through the measurement duct.

Upon pressurizing the compression chamber 70 a an amount of liquid istransiently discharged from the first side passage 24 a. The resiliencyof the second side passage 24 b results upon a pressurized discharge, ina transient flow of the liquid in the duct into the second side passage24 a. The co-operation of the two side passages and the fluidicstructures they interconnect causes the flow through the measurementduct 16 to be transiently moved sideways back and forth uponpressurizing and depressurising of the compression chamber 70 a inducedby the external actuator 26 in response to the signal raised by thedetection means 19. This transient liquid displacement, having acomponent perpendicular to the normal flow in the duct, can be appliedin deflecting particles having predetermined characteristics to separatethem from the remaining particles in the mixture.

As shown, the measurement duct 16 branches at the branch point 21 intotwo branches 22 a, 22 b and the flow rates in these branches areadjusted so that the particles normally stream through the second of thetwo branches 22 b. The angle between the branches 22 a, 22 b is between0 and 180 degrees, preferably between 10 and 45 degrees. However, theangle can even be 0 degrees, which corresponds to two parallel ductswith a straight separation wall between them.

The particles to be sorted are preferably supplied to a measurementposition in a central fluid current, which is surrounded by a particlefree liquid sheath. The process of confining a particle stream is known,and often referred to as a ‘sheath flow’ configuration. Normallyconfinement is achieved by injecting a stream of suspended particlesthrough a narrow outlet nozzle into a particle free carrier liquidflowing in the duct 16. By adjusting the ratio of flow rates of thesuspension and carrier liquid, the radial confinement in the duct aswell as the inter particle distance can be adjusted. A relative largeflow rate of the carrier liquid results in a more confined particlestream having a large distance between particles.

In a suspension introduced by the first supply duct 12, two types ofparticles can be distinguished, normal particles 18 a and particles ofinterest 18 b. Upon sensing the predetermined characteristic in aparticle 18 b in the measurement region 20, the detector 19 raises asignal. The external actuator 26 activates the first actuator bubblevalve 100 a, when signaled by the detector 19 in response to sensing thepredetermined characteristic, to create a flow disturbance in themeasurement duct 16 between the side passages 24 a, 24 b. The flowdisturbance deflects the particle 18 b having the predeterminedcharacteristic so that it flows down the first branch duct 22 a ratherthan the second branch duct 22 b. The detector communicates with theactuator 26, so that when the detector 19 senses a predeterminedcharacteristic in a particle, the actuator activates the first bubblevalve 100 a to cause pressure variations in the reservoir 70 a of thefirst bubble valve. The activation of the first bubble valves deflectsthe meniscus 25 a in the first bubble valve 100 a and causes a transientpressure variation in the first side passage 24 a. The second sidepassage 24 b and the second bubble valve 100 b absorb the transientpressure variations in the measurement duct 16 induced via the actuator26. Basically, the reservoir 70 b of the second bubble valve 100 b is abuffer chamber having a resilient wall or containing a compressiblefluid, such as a gas. The resilient properties allow the flow of liquidfrom the measurement duct into the second side passage 24 b, allowingthe pressure pulse to be absorbed and preventing disturbance to the flowof the non-selected particles in the stream of particles.

At the measurement region 20, individual particles are inspected, usinga suitable sensor means 19, for a particular characteristic, such assize, form, fluorescent intensity etc. Examples of applicable sensingmeans, known in the art, are various types of optical detection systemssuch as microscopes, machine vision systems and electronic means formeasuring electronic properties of the particles. Particularly wellknown systems in the field are systems for measuring the fluorescentintensity of particles. These systems comprise a light source having asuitable wavelength for inducing fluorescence and a detection system formeasuring the intensity of the induced fluorescent light. This approachis often used in combination with particles that are labelled with afluorescent marker, i.e. an attached molecule that upon illuminatingwith light of a particular first wavelength produces light at anotherparticular second wavelength (fluorescence). If this second wavelengthlight is detected, the characteristic is sensed and a signal is raised.

Other examples include the measurement of light scattered by particlesflowing through the measurement region. Interpreting the scatteringyield information on the size and form of particles, which can beadopted to raise a signal when a predetermined characteristic isdetected.

The actuator 26 for pressurizing the compression chamber of the firstbubble valve may comprise an external actuator that responds to a signalfrom the sensor that a particle has a selected predeterminedcharacteristic. There are two classes of external actuators that aresuitable for increasing the pressure. The first class directly providesa gas pressure to the liquid in the first side passage 24 a. Forexample, the actuator may comprise a source of pressurized gas connectedwith a switching valve to the liquid column in the side passage 24 a.Activation of the switch connects the passage to the source ofpressurized gas, which deflects the meniscus in the liquid. Upondeactivation, the switch connects the passage 24 a back to the normaloperating pressure.

Alternatively, a displacement actuator may be used in combination with aclosed compression chamber having a movable wall. When the displacementactuator displaces the wall of the compression chamber inward, thepressure inside increases. If the movable wall is displaced back to theoriginal position, the pressure is reduced back to the normal operatingpressure. An example of a suitable displacement actuator is anelectromagnetic actuator, which causes displacement of a plunger uponenergizing a coil. Another example is the use of piezoelectric material,for example in the form of a cylinder or a stack of disks, which uponthe application of a voltage produces a linear displacement. Both typesof actuators engage the movable wall of the compression chamber 70 tocause pressure variations therein.

FIGS. 2-4 illustrate the switching operation of switch 40 in theparticle sorting system 10 of FIG. 1. In FIG. 2, the detector 19 sensesthe predetermined characteristic in a particle and raises a signal toactivate the actuator 26. Upon activation of the actuator, the pressurewithin the reservoir 70 a of the first bubble valve 100 a is increased,deflecting the meniscus 25 a and causing a transient discharge of liquidfrom the first side passage 24 a, as indicated by the arrow. The suddenpressure increase caused at this point in the duct causes liquid to flowinto the second side passage 24 b, because of the resilient propertiesof the reservoir of the second bubble valve 100 b. This movement ofliquid into the second side passage 24 b is indicated with an arrow. Asa result, as can be seen in the figure, the flow through the measurementduct 16 is deflected, causing the selected particle of interest 18 blocated between the first side passage 24 a and the second side passage24 b to be shifted perpendicular to its flow direction in the normalstate. The flow resistances to the measurement duct 16, the first branch22 a and the second branch 22 b is chosen so that the preferreddirection of the flow to and from the first side passage 24 a and thesecond side passage 24 b has an appreciable component perpendicular tothe normal flow through the measurement duct 16. This goal can forinstance be reached by the first branch 22 a and the second branch 22 bso that their resistances to flow is large in comparison with the flowresistances of the first side passage 24 a and the second side passage24 b.

FIG. 3 shows the particle sorting system 10 during the relief of thefirst bubble valve reservoir when the particle of interest 18 b has leftthe volume between the first side passage 24 a and the second sidepassage 24 b. The actuator 26 is deactivated, causing the pressureinside the reservoirs 70 a, 70 b to return to the normal pressure.During this relief phase there is a negative pressure difference betweenthe two reservoirs 70 a, 70 b of the bubble valves, causing a liquidflow through the first side passage 24 a and the second side passage 24b opposite to the liquid flow shown in the previous figure and asindicated by the arrows.

FIG. 4 illustrates the particle sorting system 10 after completion ofthe switching sequence. The pressures inside the reservoirs of thebubble valves are equalized, allowing the flow through the measurementduct 16 to normalize. As the particle of interest 18 b has beendisplaced radially, it will flow into the first branch 22 a, while theother particle continue to flow into the second branch 22 b, therebyseparating the particles based on the predetermined characteristic.

This process of detecting and selective deflecting of particles may berepeated many times per second for sorting particles at a high rate.Adopting the fluid switching as described, switching operations may beexecuted up to around several thousand switching operations per second,yielding sorting rates in the order of million sorted particles perhour.

According to another embodiment of the invention, the actuator bubblevalve 100 a and the buffer bubble valve 100 b may be placed in differentpositions. For example, as shown in FIG. 5, the actuator bubble valve100 a and the first side passage 24 a and/or the buffer bubble valve 100b and the second side passage 24 b may be place upstream from the branchpoint 21. The components may be placed in any suitable location, suchthat the flow resistance between the actuator chamber 70 a and thebuffer chamber 70 b is less than the flow resistance between any ofthese latter components and other pressure sources. More particularly,the actuator chamber 70 a and the buffer chamber 70 b may be placed suchthat the flow resistance between them is less than the flow resistancebetween a selected particle and a subsequent particle in the stream ofparticles. The positioning of the components in this manner thusprevents a pressure wave generated by the above described method ofdeflecting a single selected particle, from travelling upstream ordownstream and affecting the flow of the remaining particles in thestream of particles. The larger the difference in flow resistances, thelarger the level of isolation of the fluidic switching operation withassociated pressure transients from the flow characteristics in the restof the system. Moreover, the in-situ dampening of generated pressurepulses applied for sorting allows the implementation of sorting networkscomprising a plurality of switches 40, each of which is hydraulicallyand pneumatically isolated from the others.

According to another embodiment, shown in FIG. 6, the particle sortingsystem of the invention may use any suitable pressure wave generator (inplace of a bubble valve) in combination with the buffer bubble valve 100b. For example, the pressure wave generator 260 may comprise an actuatorsuch as a piezoelectric column or a stepper motor, provided with aplunger that can act upon the flowing liquid, either directly or viadeflection of the channel system, to selectively deflect particles whenthe actuator is activated by a signal. Other suitable pressure wavegenerators include electromagnetic actuators, thermopneumatic actuatorsand a heat pulse generator for generating vapor bubbles in the flowingliquid by applying heat pulses. The buffer bubble valve 100 b ispositioned to absorb the pressure wave created by the pressure wavegenerator 260 to prevent flow disturbance in the other particles of theparticle stream. The spring constant of the buffer 100 b may be variedaccording to the particular requirements by varying the volume of thebuffer chamber 70 b, the cross-sectional area of the side passage 24 band/or the stiffness or the thickness of a flexible membrane (reference72 in FIG. 7) forming the buffer chamber 70 b.

FIG. 7 illustrates an embodiment of a bubble valve 100 suitable forcreating a pressure pulse to separate particles of interest from otherparticles in a stream of particles and/or acting as a buffer forabsorbing a pressure pulse according to the teachings of the presentinvention. As shown, the bubble valve 100 is formed adjacent to a sidepassage 24 a or 24 b formed in a substrate which leads to themeasurement duct 16. The side passage 24 a includes a fluid interfaceport 17 formed by an aperture in the side wall of the passage. A sealedcompression chamber 70 is positioned adjacent to the side passage 24 aand communicates with the side passage through the fluid interface port.The illustrative chamber 70 is formed by a seal 71 and a flexiblemembrane 72. The carrier fluid in the side passage 24 a forms a meniscus25 at the interface between the side passage and the chamber. Theactuator 26 depresses the flexible membrane to increase the pressure inthe chamber, which deflects the meniscus and causes a pressure pulse inthe carrier fluid.

FIG. 8 shows a sorting module 50 having an appropriate supply duct 52for providing a stream of particles to be sorted as well as an outletduct 54 and a second outlet duct 56 carrying the particles sorted in thesorting module 50. The sorting module 50 comprises detector system 19for sensing particles entering the sorting module 50 via the supply duct52 operationally connected to a switch 40 for providing the requiredswitching capabilities to sort particles. The first branch 22 b andsecond branch 22 a are in fluidic connection with the outlet duct 54 andsecond outlet duct 56.

FIG. 9 shows a particle sorting system 500 according to an alternateembodiment of the invention, comprising a plurality of sorting module 50operating in parallel. The individual outlet duct 54 of the sortingmodule 50 are forwarded to a first combined outlet 58, the individualsecond outlet duct 56 are forwarded to a second combined outlet 60. Theparallel arrangement of sorting modules yields a system of combinedsorting module 50 having an overall sorting rate of N times the sortingrate of an individual sorting module 50, where N is the number ofparallel connected sorting module 50.

FIG. 10 shows a particle sorting system 550 according to anotherembodiment, comprising a first sorting module 50 a and a second sortingmodule 50 b in series with the first sorting module 50 a. The secondsorting module 50 b may be equipped for sorting out particles having apredetermined characteristic different than the predeterminedcharacteristic of the particles sorted out by the first sorting module50 a. The particle stream enters the first sorting module 50 a throughthe supply duct 52 and may contain at least two types of particles. Afirst type of particles is sorted out in the first sorting module 50 aand leaves through the first outlet duct 54 a. The remaining particlesleave the first sorting module 50 a through second outlet duct 56 a andare fed into the second sorting module 50 b via the second supply duct52 b. From this stream of particles, particles having the otherpredetermined characteristic are sorted out and leave through the secondoutlet duct 54 b. Particles that posses neither of the two predeterminedcharacteristics leave the second sorting module 50 b via the secondoutlet duct 56 b.

FIG. 11 shows a hierarchical architecture for high throughput-low errorsorting according to another embodiment of the invention. The embodimentshown is a two-stage particle sorting system 800 for sorting a pluralityof parallel particles streams in a first stage, aggregating the outputsof the first stage and then performing a secondary sorting process onthe output of the first stage. An input stream of particles insuspension 80 from a particle input chamber 88 is split among N singlesorting channels 81 a-81 n, each channel being capable of sorting aselected number of particles per second. Each channel 81 includes adetection region 84 for examining the particles and identifyingparticles that have a predetermined characteristic and a switchingregion 82 for separating the particles having the predeterminedcharacteristic from the other particles in the stream, as describedabove. The switching region 82 produces two output streams of particles:a “selected” stream and a “rejected” stream in its switching region 82based on the measured particle characteristics at the detection region84. The “selected” streams from each channel are aggregated in anaggregation region 86 into one stream to be sorted again in a secondarysorting channel 810. As shown, the secondary sorting channel 810 repeatsthe sorting process of detecting and sorting based on a predeterminedcharacteristic.

Given that each single channel sorting process produces some error (y)rate (y is a probability less than one of a particle being “selected” bymistake) of mistaken selections, the hierarchical architecture producesan lower error rate of y² for a 2-stage hierarchy as drawn or y^(n) foran n-stage hierarchy. For example, if the single channel error rate is1% the 2-stage error rate is 0.01% or one part in 10⁴.

Alternatively the architecture could have M primary sets of N sortingchannels per secondary channel. Given that the application wants tocapture particles that have a presence in the input at rate z and singlechannel sorters have a maximum sorting rate x particles per second. Thesystem throughput is M*N*x in particles per second. The number ofparticles aggregated in N channels per second is N*x*z and so N*z mustbe less than 1 so that all particles aggregated from N channels can besorted by a single secondary channel. To increase throughput above N=1/zone must add parallel groups of N primary+1 secondary channels. Overallthroughput then comes from M*N*x with M secondary channels.

FIG. 12 show a parallel-serial particle sorting system 160 according toanother embodiment of the invention. The parallel-serial particlesorting system 160 includes a first parallel sorting module 161 and asecond parallel sorting module 162. The first sorting module 161 isapplied in multiple marked particles and particles having both markersare sorted out and conveyed through the exit channel 165.

FIG. 13 shows another parallel-serial particle sorting system 170. Thefirst parallel sorting module 171 separates particles having a firstmarker, collects the particles from the different channels and conveysthe particles having the first marker through the first exit channel175. All other particles are then fed into a second parallel sorter 172for sorting particles having a second marker. The particles having thesecond marker are collected and conveyed through a second exit channel176. Particles having neither the first marker nor the second marker areconveyed through a third exit channel 177.

The present invention has been described relative to an illustrativeembodiment. Since certain changes may be made in the above constructionswithout departing from the scope of the invention, it is intended thatall matter contained in the above description or shown in theaccompanying drawings be interpreted as illustrative and not in alimiting sense.

It is also to be understood that the following claims are to cover allgeneric and specific features of the invention described herein, and allstatements of the scope of the invention which, as a matter of language,might be said to fall therebetween.

1. A particle sorting system, comprising: a plurality of substantiallyparallel sorting channels formed on a substrate, and a plurality ofsorting modules, each sorting module associated with one of said sortingchannels, for distributing particles having a first predeterminedcharacteristic to a first outlet of the associated sorting channel andparticles not having the first predetermined characteristic to a secondoutlet of the associated sorting channel, each said sorting moduleincluding a sealed gas-filled reservoir disposed in the substrate incommunication with the associated sorting channel and an actuator forincreasing an internal pressure of the gas-filled reservoir toselectively modify fluid flow through the associated sorting channel toselectively deflect a particle having the first predeterminedcharacteristic into the first outlet of the associated sorting channel.2. The particle sorting system of claim 1, wherein each sorting modulefurther includes a movable membrane forming at least a portion of a sidewall of the gas-filled reservoir.
 3. The particle sorting system ofclaim 2, wherein each actuator selectively deflects the movable membraneto increase pressure in the gas-filled reservoir to modify said fluidflow.
 4. The particle sorting system of claim 1, wherein each sortingmodule further comprises a buffer for limiting said modification of thefluid flow to a region of the associated sorting channel along thesorting module and preventing flow disturbance in other regions of theassociated sorting channel.
 5. The particle sorting system of claim 1,wherein each sorting module further includes a side channel connectingthe gas-filled reservoir to the associated sorting channel.
 6. Aparticle sorting system, comprising: a plurality of substantiallyparallel sorting channels formed on a substrate, each sorting channelcapable of conveying a stream of particles in a carrier fluid, aplurality of actuators arranged external to the substrate, each actuatorassociated with a sorting channel formed on the substrate, forselectively creating a flow disturbance within the associated sortingchannel to deflect a selected particle in the stream of particles fromthe stream of particles; and a plurality of buffers, each bufferassociated with an actuator for absorbing the flow disturbance in theassociated sorting channel, wherein each buffer comprises a gas-filledreservoir in fluid communication with the associated sorting channel. 7.The particle sorting system of claim 6, wherein each sorting channelincludes a gas-filled reservoir in fluid communication therewith, andthe actuator increases an internal pressure of the gas-filled reservoirto create said flow disturbance.
 8. The particle sorting system of claim7, wherein each gas-filled reservoir includes a flexible membraneforming at least a portion of a side wall of the gas-filled reservoir,and the actuator deflects the flexible membrane to increase saidinternal pressure.
 9. The particle sorting system of claim 7, whereineach buffer is arranged opposite the gas-filled reservoir in the flowchannel.
 10. A particle sorting system, comprising: a plurality ofsubstantially parallel sorting channels formed on a substrate, and aplurality of sorting modules, each sorting module associated with one ofsaid sorting channels, for distributing particles having a firstpredetermined characteristic to a first outlet of the associated sortingchannel and particles not having the first predetermined characteristicto a second outlet of the associated sorting channel, each said sortingmodule including a gas-filled reservoir formed in the substrate having amovable wall disposed in communication with the associated sortingchannel for selectively modifying fluid flow through the associatedsorting channel to selectively deflect a particle having the firstpredetermined characteristic into the first outlet of the associatedsorting channel.
 11. The particle sorting system of claim 10, whereinthe movable wall comprises a flexible membrane.
 12. The particle sortingsystem of claim 10, wherein each sorting module further includes anassociated actuator for selectively moving the movable wall to increasean internal pressure of the gas-filled reservoir to selectively modifythe fluid flow through the associated sorting channel.
 13. The particlesorting system of claim 12, wherein the actuator selectively contactsand depresses the movable wall to increase an internal pressure of thegas-filled reservoir.